The present invention relates to a method for removing radioactive cesium from a vapor stream. In particular, the present invention relates to a method for removing radioactive cesium from high temperature steam.
It is important to provide a method for the removal of cesium in the event of a release of radioactivity in a reactor environment. Cesium includes three radioactive isotopes of which Cs-139 has a half-life of only 9.3 minutes. However, two other isotopes of cesium have an intermediate half-life. Cs-133 has a half-life of about 12 years, and Cs-137 has a half-life of about 30 years. Accordingly, a release of radioactive cesium will contaminate equipment and the plant facility for a long time.
Sufficient radioactive cesium may be released by the failure of fuel rod cladding in nuclear power reactors, such as boiling water reactors and pressurized water reactors, to create hazardous conditions which limit access to the reactor facility by the plant personnel. In some instances, the radioactive cesium may be transferred and transported by steam or some other vapor medium to various remote locations in the plant facility and thereby increase the area of concern for personnel safety.
Inorganic zeolites were successfully used to completely remove the radioactive cesium from the primary water at the TMI-2 plant subsequent to the well-known accident which had contaminated that water at Three-Mile Island. The removal, however, was from water at ambient temperatures, and not from high temperature steam. Furthermore, the zeolites break down physically in steam so as to release loose powders capable of plugging filters and other equipment downstream of the zeolite. Organic materials such as ion exchange resins are also capable of removing cesium ions, but they are damaged by radiation, thereby making them also unacceptable for removing radioactive cesium from a hot vapor such as 750.degree. F. steam.
Cesium and its compounds are volatile at temperatures above 700.degree. F., and are not easily removed in a demisting device or an aerosol filter. It appears in the hot steam as CsI and CsOH species.
Accordingly, it is an object of the present invention to remove the various isotopes of cesium from a hot vapor stream either by chemical combination or by physical combination, or by both.
It is another object of the present invention to remove the various isotopes of cesium from a hot vapor, such as 750.degree. F. steam, in the various forms in which the cesium could exist.
It is yet another object of the present invention to remove the various forms of radioactive cesium from a high temperature vapor stream, such as steam, in a bed of particulate matter which will retain the radioactive cesium.
It is a further object of the present invention to achieve the removal of radioactive cesium from a high temperature vapor stream in a bed of particulate matter which has a physical form that will produce an acceptably low pressure drop when placed inside of a closed vapor system, such as a steam circulating system.
It is a still further object of the present invention to provide a bed of particulate matter for the removal of cesium from high temperature steam which has physical integrity in the dynamic high temperature steam system, so that the bed will not break up to release powdery substances which could plug filters and other equipment within the steam piping system.
It is an additional further object of the present invention to provide a particulate matter which will remove radioactive cesium from high temperature steam, whereby the particulate matter will withstand break-down, both physical and chemical, under the intense gamma radiation emitted by the radioactive isotopes of cesium and other fission product isotopes present in the circulating steam system.
These and other objects of the invention, as well as the advantages thereof, will become clear from the disclosure which follows.